Metabolism and Volatile Compound Profile of Long-Shelf-Life Tomatoes Produced in the Field and Greenhouse After Postharvest Ethanol Treatment

The objective of this study was to evaluate the effect of postharvest ethanol treatment on the metabolism and production of volatile compounds in long-shelf-life (LSL) tomato fruit grown under two systems: open-field and greenhouse. After harvest, fruits were stored in 25 L chambers at 20 °C for the application of the following ethanol treatments: (1) control (chambers containing samples were only sealed); (2) 200 mg L−1 ethanol; (3) 400 mg L−1 ethanol; (4) 600 mg L−1 ethanol; and (5) 800 mg L−1 ethanol vapor. Ethanol was applied to a paper towel (0.2 × 0.2 m) in liquid form, and the chambers were then hermetically sealed for 24 h for ethanol volatilization and absorption by the tomatoes. After treatment, fruits were kept for 10 days at 20 °C until quality analyses were performed. ACC oxidase activity, respiration rate, and ethylene production were significantly affected by ethanol treatments and the cultivation system. ACC oxidase activity was higher in the field than in the greenhouse, but ethylene production and respiration rate were lower. Under open-field conditions, higher ethanol doses resulted in greater ethylene production but reduced the respiration rate. Tomatoes treated with ethanol had increased concentrations of most volatile compounds, particularly at higher doses of 600 mg L−1 in the greenhouse and 800 mg L−1 in field conditions. Volatile compounds that increased with ethanol treatment in the greenhouse included acetaldehyde, ethyl acetate, hexanal, and especially hexanoic acid, while ethyl propanoate, hexyl acetate, 2-methylbutanal, and citral increased in field conditions. On the other hand, the lower ethanol doses (200 mg L−1) in greenhouse conditions were associated with lipid metabolism degradation compounds such as E-2-hexenal, E-2-hexenyl acetate, citral and butanal; another metabolic process likely contributed to this increase in greenhouse conditions. Furthermore, ethanol did not accumulate in the fruit pulp, indicating its bioconversion into other volatile compounds that significantly improve the flavor and aroma of LSL tomatoes, potentially enhancing consumer acceptance.